The present invention relates to a joining device for the joining, in particular the welding, of two parts one to the other, having a joining head comprising a lifting device for linear transport of a joining unit along a lift axis relative to the joining head, said joining device performing a joining operation by transporting the joining unit out of a lift position towards a base position, and the joining unit comprising a boom extending outside of the joining head, at the free end of which the joining operation takes place offset parallel to the lift axis. The invention relates further to a process for the joining, in particular the welding, of two parts one to the other, comprising the following steps: transport of a joining unit relative to a joining head into a lift position by means of a lifting device in order to join the parts one to the other towards a base position of the joining unit, and transport of the joining unit into the base position.
Such a joining device and such a joining process are disclosed in EP 0,367,414 B1. By joining, in the production engineering sense, is meant a process of positive geometrical, dynamic or material connection of two or more parts, or of parts to an amorphous material, by juxtaposition (e.g. insertion, encasement), pressing on or into (e.g. screwing, wedging, shrinking), material connection (e.g. welding, soldering, bonding), molding (e.g. fusing, casting), transforming (e.g. rolling) or filling (e.g. impregnating an electrical winding).
In short-time electric arc welding, an element is welded onto a part. Thus, an electric arc is set up between the element and the part, incipiently fusing the frontal surfaces. Then the element and the part are moved towards each other so that the melts mingle. The arc is short-circuited and the whole melt solidifies. It is possible to draw the electric arc (lift ignition). Here, the element is first placed on the part (base position). Then a pilot current is switched on, and the element is lifted relative to the part up to a desired level (lift position), thus drawing an arc. Only then, the welding current is switched on and the element is replaced on the part, whereupon the melts mingle. Then the welding current is switched off, so that the entire melt solidifies.
To obtain uniformly good welding results, it is important, among other things, to find the relative position between element and part, in particular to lift the element to the correct level before the welding current is switched on. For this purpose, as a rule each welding operation is preceded by a measurement of the relative position, particularly in the form of a zero position determination. This is especially important in the case of robot-based systems. True, present-day robots are generally able to position with comparative precision. High precision, however, especially owing to the large masses in motion, is not available with very high dynamics. Ordinarily, the robots have a scope of motion in three coordinates. In the simplest case, a robot is an automatically driven linear guide (carriage) on which a welding head is mounted. As a rule, such a carriage is attached to the arm of a multi-axial (bent arm) robot.
In the automotive industry, bolt welding systems are employed. There they serve primarily to weld elements such as threaded or unthreaded bolts, eyes, nuts, etc. onto the body sheet-metal. These elements then serve as holding anchors for attachment, for example, of interior trim, cable trees or the like. In the automotive industry, speed of production is an essential consideration. Within a few minutes, hundreds of elements are to be welded on in various positions automatically by means of robots. The robots must consequently move with high dynamics.
Thus, it is known that a welding head base bearing a carriage may be attached to the arm of a robot. The carriage is high-dynamically movable, commonly by means of a pneumatic or hydraulic system. On the carriage, the welding head proper is mounted, in turn possessing a lifting device to move the element with high precision. To determine the relative position between the element and the part, it is known that a so-called support foot may be attached to the welding head (for example, “Neue TUCKER-Technologie. Bolzenschweissen mit System,” Emhart Tucker, September 1999).
The spatial size of a welding head, however, represents a natural spatial barrier within which bolt welding with welding heads is possible. So that bolts can be welded in locations of difficult access as well, there are welding heads known in the prior art that are connected to a welding gun by way of an extension cable. Such a welding head is disclosed in DE G 94 17 371. The welding head of DE G 94 17 371 is much smaller than the welding gun connected to it. This welding head is suitable for applications where not much room is available. A disadvantage of this type of bolt welding is that the welding device must be operated by hand. Both the welding gun and also the welding head connected by way of an extension must be positioned and actuated manually by a worker. This is time-consuming. It is also reflected in high production costs, operating labor being costly as a rule.
Hence, one object of the invention is to create a joining device and a process whereby automated joining can be accomplished even in positions difficult of access. This object is accomplished by a joining device of the kind initially mentioned, wherein the joining unit is so oriented relative to the joining head that the joining unit is extended in the lift position. Further, the object is accomplished by a process for joining of the kind initially mentioned, wherein the joining unit is extended into the lift position relative to the joining head.
In this way, it is brought about that even positions of difficult access can be reached automatically with a joining head for purposes of joining. The invention makes it possible, by contrast with the prior art, to join ‘rearward.’ The ‘rearward’ orientation will be explained in the following. Besides, time and expense can be saved. The device and the process according to the present invention open up a multitude of applications in which but little space is available for joining.
It is preferred as well for the joining unit to be so oriented relative to the joining head that the joining device is run into the base position. According to a preferred embodiment, the joining head comprises a holding device for holding one of the parts. Further, it is preferred for a held part to be a bolt and the holding device a bolt holder. Also, it is advantageous if the joining head is a welding head. Through these measures, it is possible to utilize the joining device as an arc welding device, capable in particular of welding bolts to a part.
According to another preferred embodiment, the joining head comprises a support foot. An additionally provided support foot facilitates the positioning of the joining head relative to the part to which the other part is attached. Further, it is preferred for the joining head to be attached to a carriage. Thus, it is possible rapidly to transport the joining head, and with it the joining unit, into the base position.
According to another embodiment, the joining device further comprises a part feed, in particular an element feed. This likewise will enhance the speed of an operating cycle, since parts can be supplied automatically rather than manually. It has also proved advantageous for the lifting device to comprise a compression spring, to be wound by means of a linear motor. Moreover, the linear motor is extended in the lift position. Through these measures, it is possible to weld ‘rearward.’ It will be understood that the features aforementioned and those yet to be illustrated below may be employed not only in the particular combination specified but also in other combinations, or alone, without departing from the scope of the present invention.